Directional radio beacon



2, H43. A. H. HERMANSSON DIRECTIONAL RADIO BEACON Filed Dec. 11, 1940 s Sheets-Sheet 1 jINVENTOR @ATTORNEY A. H. HERMANSSON DIRECTIONAL RADIO BEACON Feb;

Fi led Dec. 11, 1940 3 Sheets-Sheet 2 c; ya r J I I 6 A M C m m Y 20 B I M 4 U f Wm I M0 4 no Z M an A4 P 0 M W 4 V, w c w a EM. 2,, W43. A, H, HERM NSSQN 2310mm DIRECTIONAL RADIO BEACON Filed Dec. 11, 1940 s Sheets$heet s 76 W M %ENTOR. BY 4;;

ATLYLORNEY Patented Feb. 2, 1943 2,310,079 DIRECTIONAL RADIO BEACON Adolf Harald Hermansson, Stockholm, Sweden,

assignor to Aga-Baltic Radio Aktiebolag, Stockholm, Sweden, a. corporation of Sweden Application December 11, 1940, Serial No. 369,580 In Sweden January 4, 1940 6 Claims.

My invention relates to directional radio beacons.

Directional radio beacons are known in which the direction of transmission is reversed in a predetermined sequence, usually either in time with the code letters e and t or a and n or sometimes in time with other code letters. A listener on one side of a certain plane through the radio beacon will only hear the letter e (or a) whereas a listener on the other side of this plane will only hear the letter t (or 11). If the listener passes from one side of the plane to the other he will pass a certain position, viz. the said plane, where both signals are heard with equal intensity. As these signals were formed by shifting the phase characteristic of the directional beacon, the signals will complete each other so that a continuous tone is heard indicating that the listener is in the desired plane.

These radio beacons are usually called E-T- beacons. The directional sharpness is as a rule very good with such radio beacons and for this reason they are growing to be used more and more for indicating courses on land, on sea or in the air. Although the E-T-beacons offer a relatively high directional sharpness they have also certain disadvantages. Especially prominent is the dimculty of building phase shifting apparatus with sufiicient precision. Phase shifters used hitherto have as a rule been rather complicated and it was necessary to make them of rather high precision in order to obtain the high directional sharpness. These circumstances have substantially retarded the commercial use of E-T-beacons.

The precision of observation of a beacon of the above mentioned type is greatly decreased if, at the moment of phase shifting when the greatest attention is required to determine the change in sound intensity. there is also obtained a momentary pulse of higher sound intensity which has nothing to do with the normal function of the beacon. The present invention bases upon the discovery that this pulse of sound results from a momentary change of load at the moment of phase shifting.

In the drawings:

Fig. 1 is a schematic diagram of a directional radio beacon embodying the present invention;

Fig. 2 is a polar diagram illustrating the operation of the radio beacon of Fig. 1;

Fig. 3 is a diagram illustrating the operation of the phase shifting means embodying the present invention;

Figs. 4 and 5 are schematic diagrams of directional systems embodying the present invention;

Figs. 6 and 7 are diagrams illustrating the operation of the phase shifting mechanism; and

Fig. 8 is a detail view of the phase shifting condenser plates embodying the present invention.

For explanation of these circumstances reference is made to Fig. 1 of the annexed drawings. The transmitter is indicated II. This is connected through a phase shifter 2 to a loop antenna l3, and through a transformer hi to a non-directional antenna 15. The phase shifter contains a set of fixed condenser plates which are actuated by a code-mechanism [6 in time with the code latters e and t.

The operation of the arrangement is shown in Fig. 2. The characteristic of the non-directional antenna is indicated by the curve 11, and the characteristic of the directional antenna by the curve I8. Both of the characteristics combine to form a directional characteristic [9. It is assumed that the part of the characteristic l8 drawn in full lines is in phase with the characteristic I1, whereas the part of the characteristic l8 drawn in dot and dash lines is in counter-phase. The shifting of the phase of the current in the loop antenna 13 also shifts the phase of the characteristic [8, and causes the system to have the characteristic 20.

In the phase shifting takes place in time with the code letters e and t, which complete each other, a listener located in the direction 2| from the beacon will hear the letters e with an intensity represented by the point 22 in the diagram, and the letters t with an intensity represented by the point 23. If the listener shifts to the direction 24 in'the diagram, he will obviously hearthe letters e and t with the same intensityfrepresented by the point 25.

In systems of this type the listener tries to find a direction in which a continuous tone is heard. However, it has not been possible to avoid an accidental change of load in the circuits which feed the loop antenna I 3 at the time of change over of the movable condenser plate from one of the fixed condenser plates to the other. If the movable condenser plate is less than or equal to the space between the two fixed condenser plates, which is the usual case, the load on the transmitter H becomes a minimum at the moment when the movable condenser plate of the phase shifter is exactly between the fixed condenser plates. This causes a change of impedance in the conductor 26 feeding the antennas, anddue to this change of impedance, the

intensity of the field propagated from the antenna I will change, for instance in such a direction that it increases from the value l'l, Fig. 2, to the value 21.

This increase occurs, as mentioned above, at the moment when one is listening for a possible change of sound intensity, in order to decide if one is in the direction 24 or in any direction different therefrom, and as evident from the diagram there occurs due to the increased intensity at change over a tendency for error within an angle limited by the lines 28 and 29. It is evident from Fig. 2 that the precision is thus reduced.

According to the present invention the phase shifter is provided with a compensation circuit 39, so arranged in relation to the directional antenna i3 that each change of load in the antenna circuit caused by the phase shifter, is substantially compensated by a change of load'in a corresponding direction in the load circuit 30, so that the load of the circuit 26 remains substantially constant in magnitude and phase regardless of the changes of load caused by the phase shifter. schematically the arrangement is shown in Fig. 1 in the form of two condensers 3| and 32 mechanically connected to the movable condenser plates 33 and 34 in the phase shifter, and so adjusted that the capacity of each of the condensers 3| and 32 increases simultaneously with and to an equal extent with the decrease in capacity between the movable plates 33 and 34 and their corresponding fixed plates. The condensers 3| and 32 are further connected to a load circuit, containing for example an induction coil 35, a condenser 33 and a resistor 31, which are so adjusted in relation to each other that, together with the condensers 3i and 32, they correspond in phase and magnitude to the directional antenna I3 and to the capacities formed by the movable plates 33 and 34.

In Fig. 3 the course in the phase shifter is graphically shown, assuming that the different condenser plates are so made that the capacity variation with respect to the angle of the phase shifter takes the form of a sine curve. The curve 33 represents the capacity between the rotor plate 33 and one of the stator plates, for instance the stator plate 39 in Fig. 1, whereas the curve 40 represents the change of capacity between the rotor plate 33 and the other stator plate ill in the phase shifter. The curve 42 represents the difference between the curves 38 and 40. The curve 42 passes through zero value midway of the gap of the phase shifter represented between the positions 33 and 44. A momentary compensation of the load is also produced by means of the circuit 30 as the capacities of the condensers 3| and 32 increase according to curves 45 and 46, respectively. The difference between the curves 45 and 43 is represented by the curve 41.

For further explanation of the operation of the phase shifter to compensate for the variation of the load of the transmitter reference may be made to Figures 4, 5, 6 and 7.

In Fig. 4 a phase shifter of the same kind as shown in Fig. 1 is arranged, the drawing, however, showing schematically the balanced relationship of the phase shifter between the antenna I3 and the load 30. 1

The capacity between the movable part 33 of the phase shifter and its fixed part 39 has been denominated C1, and the capacity between the movable part 33 and the fixed part 4! has been denominated C2. The capacities between the movable part in the phase shifter coupled to the load 30, and the corresponding fixed plates have been denominated C3 and C4.

In schematic diagram the different capacities C1 and C2 as well as the different capacities Ca and C4 form a bridge coupling as indicated in Fig. 5. Upon movement of the phase shifter the capacity C1 alternatively becomes a maximum as the capacity C2 becomes zero, and the capacity C2 becomes a maximum as the capacity C1 becomes Zero. A corresponding variation takes place in the capacities C3 and C4. It is thus evident that the voltage fed to the antenna I3 is reversed. In the diagram, Fig. 5, for convenience, one of the terminals of the transmitter has been denominated and the other terminal of the transmitter When the capacities C2 are Zero the antenna circuit is completed from the transmitter l I through the capacities C1 and current flows in the antenna from left to the right as seen in Fig. 5. When the capacities C1 are zero a corresponding circuit is completed through the capacities C2, and the current flows through the antenna in the direction from the right to the left.

During the intermediate position, when neither Ci nor C2 is :zero, however, the positive terminal of the transmitter will be connected to one side of the antenna over the condenser C1, whereas the other side of the transmitter will be connected to the same side of the antenna over the condenser C2. If the grounded midpoint of a transmitter output side is used as a zero voltage point, and if the voltage over each half part of the transmitter is indicated as E, the impressed voltage on the antenna will obviously be or in other words proportional to (Ci-C2). This shows that the coupling between the transmitter and the antenna is determined by the difference between the two capacities, which was shown as the full-line curve 42 in Fig. 3.

In a corresponding manner the coupling between the transmitter and the load 33 is deter mined by the difference between the capacities C3 and C4, which is shown in Fig. 3 as the fullline curve 41.

It is possible mathematically, on the basis of the diagram shown in Fig. 5, to calculate the conditions for a constant load on the transmitter. If we introduce C1=a1+b1f1(0) and Cs: aa-i-bafaifi), respectively, in which formulas or, in, as and I); represent arbitrary constants, and 0 is the turning angle of the phase shifter, we obtain as a condition for constant load of the transmitter:

In this formula K means an arbitrary constant. The condition according to this formula may of course be fulfilled for any arbitrary function f1(0), as one has only to solve the equation,

knowing this function, with reference to f2(0).

A very simple solution is obtained, however, if one introduces:

h h 2 a a a In this equation the members (11, b1, as and b3, are arbitrary constants which are dependent upon the mechanical structure of the phase shifter, and if the part of the phase shifter coupled to the antenna, and the part coupled tothe tion 54 to the position 54 in Fig. 3.

load, have the same characteristics the condition for constant load is reduced to the formula:

b2 a l/f1 2/ +/f3( K or after elimination of all of the constants:

/f1( +/fa( This last named formula is well known. It is satisfied by:

f1(0) =cos 13(0) =sin 6 Referring now to Fig. 4, it is possible with the aid of the above equations to determine how the plates of the different condensers C1, C2, C3 and C4 should be divided. It may be assumed that the movable plates are connected to the driving shaft of the phase shifter in symmetrical relation to each other. In a diagram in Fig. 6 showing the 360 electrical degrees embraced by the movement of the phase shifter the two rotor plates are shown as 5'! and 58. The fixed plates coupled to the antenna are indicated 59 and 60, and the fixed plates coupled to the load are indicated BI and 62. If now the diagram of Fig. 6 is out along the zero-position and developed in a plane, one obtains instead the diagram shown in Fi '7.

A phase shifter embodying the arrangement of Fig. 7, is shown in Fig. 8, the movable part 51 corresponding to the stator plates 63, 64, 55 and 65, Whereas the movable part 58 corresponds to the stator plates El, 68, 69 and m. In the same manner the fixed plates 5-9 and 66 correspond to the rotor wings "H, l2, l3 and It, whereas the plate 6| in Fig. '7 corresponds to the plates and 76 in Fig. 8, and the two half plates 62 in Fig. 7 correspond to the two half plates 11 and i8 and also 19 and Eli, respectively, in Fig. 8.

Both of the rotors are applied on the same shaft. They function in the following manner: The stator plates 63, 64, 65 and 55, Fig. 8, have a span of exactly one-eighth of a revolution. On the other hand the rotor plates ll-l2 and it- 4M are made of double the width, but are divided into two wings each of which have the same form. Due to the position of these wings the capacity of the wing 12 to the stator plate 66 will decrease with exactly the same speed as the capacity of the wing ll to the stator plate 65 increases during the movement from the posi- The total capacity between the wings H and E2 on one side, and the stator plate 56 on the other side, will thus remain constant until the position 54, shown in Fig. 3 is reached, when the wing 12 leaves the stator plates 65 and begins to enter between the stator plates 63. Simultaneously the wing H begins to leave the space between the stator plates 66, so that the capacity of the rotor to these stator plates decreases.

Disregarding the possible edge capacities, the form of the wing H, l2, l3 and M which will produce the sine characteristic shown in Fig. 3 will be obtained by laying out in radial direction distances which are determined according to a square root function, that means according to the formula dinate system, and R means the inner diameter of the stator. k finally is a constant.

The rotor plates 15-89 are of a corresponding shape. Due to the phase displacement between the capacity changes of the phase shifter and the compensating capacity changes in the condensers 3| and 32, the rotor l58il will take the form shown at the lower right corner of Fig. 8, whole wings l5 and 16 being diametrically opposed with half wings T1 and 18, and i9 and 80, respectively on opposite sides thereof.

Beginning from the position shown in Fig. 8, it is evident that the wing H is in capacity relation to the stator plate 66 when the wing I2 is in the middle of the gap between the stator plates 66 and 63. Also the wing 79 is in the gap between the stator plate 7!] and El while the left half of the wing it is in capacity relation to the stator plate 70. The wing 88 is in capacity relation to the stator plate 69 and, due to the symmetry, the capacities between the rotor and each of the stator plates Bl69 and 63-43 are equal, so that the capacity difference becomes zero.

Upon the continued turning of the rotors the real phase shifting takes place. Simultaneously the wing 80 is turned from capacity relation to the plate 69, whereas the wing 76 is turned fully into capacity relation to the stator plate 10, so that after rotating through an angle of 22.5 the capacity between the rotor and the stator plates 68 and 1E] obtains maximum value. whereas the capacity between the rotor and th stator plates 61 and 69 becomes zero. The capacity difference has thus reached its maximum value. During the next rotation of 22.5, however, the wings 18 and 19 will be brought into capacity relation to the stator plates 69 and 6?, whereas the half wing 76 leaves its capacity relation to the stator plates Iii. Consequently capacity balance is again obtained and the capacity difference becomes zero at the moment when the phase shifting is completed. The capacity relations now remain constant during rotation through an angle of before the next phase shifting period begins. During the same time the capacity to the plates BI and 62 remain constant. This is also evident because the part of the wing 16 remaining in capacity relation to the stator plate 70 is congruent with the wing 89. Consequently I the capacity between the wing H5 and the plate H3 is decreasing at exactly the same rate as the capacity between the wing and the plate 10 is increasing. In this manner the rotation continues for 22.5 until the wing 75 has fully left the plates "m, and the wing 89 has entered between these plates. During the next 22.5 the wing 80 will move fully into capacity relation to the plates 19 whereas on the other side the wing '39 will finally leave its capacity relation to the plates 67, its capacity decreasing as the capacity of the plate 16 entering into capacity relation to the plates 61 increases.

The phase shifting is thus completed and the position is now the same as the starting position, except that due to the four-symmetry in Fig. 8 all of the parts are rotated by 90.

What is claimed is:

l. A directional radio beacon comprising a transmitter, a non-directional antenna and a directional antenna fed thereby, phase shifting means connected between said transmitter and one of said antennas to periodically reverse the phase relationship of the emitted Waves for reversing the direction of transmission, an artificial load circuit, coupling means actuated in synchronism with said phase shifting means to couple said load circuit to said transmitter, said phase-shifting means and said coupling means being so related that the impedance of said load circuit and said coupling means corresponds at all times in magnitude and phase to the impedance of said phase shifting means and the antenna connected thereto, whereby a constant load is maintained on said transmitter during the periods of phase shifting.

2. A directional radio beacon comprising a transmitter, a non-directional antenna and a directional antenna fed thereby, a phase shifting means connected between said transmitter and one of said antennas to periodically reverse the phase relationship of the emitted waves for reversing the direction of transmission, an artificial load circuit, variable coupling means actuated in synchronism with said phase shifting means to couple said load circuit to said transmitter, said phase shifting means being formed to have a cosine phase-shifting characteristic and said coupling means being formed to have a sine characteristic, whereby a substantially constant load is maintained on said transmitter during the period of phase shifting.

3. A directional radio beacon comprising a transmitter, a non-directional antenna and a directional antenna fed thereby, a phase shifting means connected between said transmitter and one of said antennas to periodically reverse the phase relationship of the emitted waves for reversing the direction of transmission, an artificial load circuit, variable coupling means actuated in synchronism with said phase shifting means to couple said load circuit to said transmitter, said phase shifting means and said coupling means each comprising condensers having stator and rotor plates shaped to provide characteristics suited to maintain a substantially constant load on said transmitter during the period of phase shifting.

4. A directional radio beacon comprising a transmitter, a non-directional antenna and a directional antenna fed thereby, a phase shifting means connected between said transmitter and one of said antennas to periodically reverse the phase relationship of the emitted waves for reversing the direction of transmission, an artificial load circuit, variable coupling means actuated in synchronism with said phase shifting means to couple said load circuit to said transmitter, said phase shifting means and said coupling means each comprising condensers having stator and rotor plates extending over substantially electrical degrees, one of said plates being formed by two symmetrically arranged wing shaped parts shaped to provide characteristics suited to maintain a substantially constant load on said transmitter during the period of phase shifting.

5. A directional radio beacon comprising a transmitter, a non-directional antenna and a directional antenna fed thereby, a phase shifting means connected between said transmitter and one of said antennas to periodically reverse the phase relationship of the emitted Waves for reversing the direction of transmission, an artificial load circuit, variable coupling means actuated in synchronism with said phase shifting means to couple said load circuit to said transmitter, said phase shifting means and said coupling means each comprising condensers having stator and rotor plates extending over substantially 90 electrical degrees, one of said plates being formed by two symmetrically arranged wing shaped parts, each of said wing parts being shaped according to a square root function so as to provide characteristics suited to maintain a substantially constant load on said transmitter during the period of phase shifting.

6. A directional radio beacon comprising a transmitter, a non-directional antenna and a directional antenna fed thereby, a phase shifting means connected between said transmitter and one of said antennas to periodically reverse the phase relationship of the emitted waves for reversing the direction of transmission, an artificial load circuit, variable coupling means actuated in synchronism with said phase shifting means to couple said load circuit to said transmitter, said coupling means comprising a condenser having stator and rotor plates, said stator plates extending over substantially 90 electrical degrees, said rotor plate extending over substantially electrical degrees and being divided into three wing shaped parts, the outer wing parts having an extension of about 45 electrical degrees each and the center wing parts having an extension of about 90 electrical degrees, all of said wing parts being shaped according to a square root function.

ADOLF HARALD HERMANSSON. 

